Patent GB-1394633-A (GB)
Title: Brakes
Inventor: NEHR C W
IPC: F16D65/14
Filed: 1973-09-06
Abstract: 1394633 Drum-brake actuators; slack-adjusting ROCKWELL INTERNATIONAL CORP 6 Sept 1973 [19 Oct 1972] 41924/73 Heading F2E In a wedge-actuator housing 24, Fig. 2, for an internal shoe drum brake, incorporating plunger assemblies 32, 34, one of which, 32, includes a threaded-nut-and-stud assembly 82, 94, Fig. 4, as part of a slack-adjusting mechanism, the nut 82 has a partially-threaded bore, the threads being formed on a first portion of less diameter than a second portion, and means for limiting travel of the stud 94 relative to the nut 82 to prevent their disengagement comprises a snap ring 136 received in a circumferential groove 134 in the stud, the outer diameter of the snap ring being intermediate in magnitude between the diameters of the two bore portions so that it cannot enter the threaded portion of the bore. As shown, plunger assemblies 32, 34, Fig. 2, are moved apart to apply the brake shoes to the drum (not shown) when a push rod 54 is moved inwardly of the housing 24 by fluid pressure or a lever linkage (not shown) so that wedge 56 and rollers 48, 50, are consequentially moved inwards, in known manner. The plunger assembly 32 has a plunger member 76 relative to which a nut 82 is axially located but rotatable, and a stud 94, Fig. 4, threaded in the nut is axially movable but non-rotatable. The nut 82 has spiral teeth 84, Fig. 4, on its outer surface which co-operate with a toothed pawl and guide 80, Fig. 2. The spacing and spiral angle of teeth 84 are so selected that pawl 80 will only ride up on them during normal braking operations, but will jump one tooth on operation after appropriate lining wear in known manner; on return movement of the plunger assembly, the pawl, now fully engaged, forces nut 82 to turn, thereby advancing stud 94 outwardly, also in known manner. Outward movement of stud 94 is limited by engagement of the snap ring 136, located in groove 134 in the stud, with a radial shoulder 132 in nut 82 as seen in Fig. 4. The whole of the internally-threaded portion of nut 82 is engaged with some part of stud 94 throughout the whole range of slack adjustment, so the strength of the plunger assembly is maintained constant throughout the range. The outer end of stud 94 has a star wheel formation 96 and a surface 98 against which the web (not shown) of the appropriate brake shoe bears. A rectangular clip 102 has the ends 104, 106, of its greater dimension bent over the edge of the star wheel and serving to retain a leaf spring 112 abutting against the star wheel. The shoe web extends through an aperture 103 in clip 102 and thus prevents the clip, and hence spring 112 and stud 94, from rotating, normally. However, manual adjustment of the position of stud 94 may be effected by inserting a tool between the teeth of the star wheel to rotate it, the resistance of spring 112 being overcome. Where only one actuator is provided between one pair of shoe ends, the other pair of shoe ends being anchored, plunger assembly 34, Fig. 2, is provided with an adjusting mechanism in the same way as 32. Where there are two actuators, each has only one adjuster.